<script src="https://unpkg.com/vue"></script>

<div id="watch-example">
  <p>
    Ask a yes/no question:
    <input v-model="question">
  </p>
  <p>{{ answer }}</p>
</div>

<!-- Since there is already a rich ecosystem of ajax libraries    -->
<!-- and collections of general-purpose utility methods, Vue core -->
<!-- is able to remain small by not reinventing them. This also   -->
<!-- gives you the freedom to just use what you're familiar with. -->
<script src="https://unpkg.com/axios@0.12.0/dist/axios.min.js"></script>
<script src="https://unpkg.com/lodash@4.13.1/lodash.min.js"></script>
<script>
  var watchExampleVM = new Vue({
    el: '#watch-example',
    data: {
      question: '',
      answer: 'I cannot give you an answer until you ask a question!'
    },
    watch: {
      // 如果 question 发生改变，这个函数就会运行
      question: function (newQuestion) {
        this.answer = 'Waiting for you to stop typing...'
        this.getAnswer()
      }
    },
    methods: {
      // _.debounce 是一个通过 lodash 限制操作频率的函数。
      // 在这个例子中，我们希望限制访问yesno.wtf/api的频率
      // ajax请求直到用户输入完毕才会发出
      // 学习更多关于 _.debounce function (and its cousin
      // _.throttle), 参考: https://lodash.com/docs#debounce
      getAnswer: _.debounce(
        function () {
          if (this.question.indexOf('?') === -1) {
            this.answer = 'Questions usually contain a question mark. ;-)'
            return
          }
          this.answer = 'Thinking...'
          var vm = this
          axios.get('https://yesno.wtf/api')
            .then(function (response) {
              vm.answer = _.capitalize(response.data.answer)
            })
            .catch(function (error) {
              vm.answer = 'Error! Could not reach the API. ' + error
            })
        },
        // 这是我们为用户停止输入等待的毫秒数
        500
      )
    }
  })

</script>
